1. Field of the Invention
The present invention relates to hybrid mode waveguide or feedhorn antenna and, more particularly, to hybrid mode waveguide or feedhorn antenna comprising a waveguide body including a first section of uniform cross-section and a second section which for the waveguide comprises a uniform cross-section and for the feedhorn antenna flares outward towards the mouth of the feedhorn, and a spiro-helical projection bonded to a dielectric layer on the inner surface of the waveguide or feedhorn antenna comprising a helically wound, dielectrically coated wire structure which in the first section of the waveguide body changes guage in a decreasing manner in each of a plurality of sequential portions thereof as the structure progresses from the throat of the waveguide towards the second section and in the second section can comprise helical turns of uniform gauge wire or helical turns of decreasing gauge sections as the structure progresses from the first section to the mouth of the waveguide or feedhorn antenna.
2. Description of the Prior Art
Hybrid mode corrugated horn antennas have been in use in the microwave field for a number of years. Various techniques for forming the corrugated horn antennas have been used to provide certain advantages. For example, U.S. Pat. No. 3,732,571 issued to N. W. T. Neale on May 8, 1973 discloses a microwave horn aerial which is corrugated on its inner surface, defining a tapered waveguide mouth area, with at least one spiro-helical projection which can be produced by a screw cutting operation with a single start spiro-helical groove or by moulding on a mandrel which can be withdrawn by unscrewing it.
In U.S. Pat. No. 3,754,273 issued to Y. Takeichi et al on Aug. 21, 1973, a circular waveguide feedhorn is disclosed which includes corrugated slots on the inner wall surface, the width of the slots abruptly changing from a smaller value in the portion near the axis of the waveguide to a larger value in the remaining portion of the slot.
In U.S. Pat. No. 4,106,026 issued to N. Bui-Hai et al on Aug. 8, 1978, a corrugated horn of the exponential type is disclosed with corrugations whose depth increases exponentially from the throat of the horn towards its mouth.
In the typical prior art arrangements, construction is generally complicated and expensive with the possible exception of the Neale feedhorn described hereinbefore, and coupling to a dominate mode waveguide is difficult and limited in bandwidth.
The problem remaining in the prior art is to provide a hybrid-mode waveguide section or feedhorn of a design which is inexpensive to fabricate, provides simplified mode coupling of the TE.sub.11 mode to the HE.sub.11 mode, and is operative over a very wide frequency bandwidth.